Methods for electroplating solder

ABSTRACT

A consumable solder anode being an anode shaped body composed of an alloy of 5 to 100 percent high purity tin and 0 to 95 percent high purity lead with approximately 50 p.p.m. of a grain refiner such as calcium, phosphorous, tellurium, sulfur.

United States Patent [191 Manko 1 Feb. 19, 1974 METHODS FOR ELECTROPLATING SOLDER [52] US. Cl 204/43 S, 75/166 D, 75/175 R,

204/54 R, 204/293 [51] Int. Cl. C23b 5/14, C23b 5/38, C23b 5/40 [58] Field of Search... 204/293, 43 S, 54; 75/175 R,

[56] References Cited FOREIGN PATENTS OR APPLICATIONS 718,982 11/1954 Great Britain 75/175 R OTHER PUBLICATIONS Equilibrium Data for Tin Alloys, Tin Research Insti tute, (1949), p. 16.

Primary ExaminerG. L. Kaplan Attorney, Agent, or Firm-Popper, Bain, Bobis, Gilfillan & Rhodes [5 7 ABSTRACT A consumable solder anode being an anode shaped body composed of an alloy of 5 to 100 percent high purity tin and 0 to 95 percent high purity lead with approximately 50 p.p.m. of a grain refiner such as calcium, phosphorous, tellurium, sulfur.

4 Claims, No Drawings BACKGROUND OF THE INVENTION 1. Field of Invention This invention relates generally to consumable solder anodes, and particularly to consumable solder anodes which display a high degree of resistance to intergranular corrosion in electrolytes of either low or high pH, which do not proliferate surface accumulations of insoluble reaction products, and which are capable of sustaining high current density for fast plating, without the aforementioned surface accumulations, corrosion or necking.

2. Description of the Prior Art Cast solder anodes are in wide general use. In casting anodes, an intergranular structure is achieved which is particularly subject to chemical attack by aggressive electrolytes which may be of either high or low pH. The anodes rapidly deteriorate because whole grains are eaten around until they are physically unsupported and become discharged from the surface of the anode. Also, the anode is said to be necked, i.e., it is more rapidly eaten away at its upper end at the level of the surface of the electrolyte, until the main body portion of the anode is only supported by a thin connecting neck; hence the term necked.

When necking occurs, the anode cannot support high current density throughout its entire structure without heating at the neck, so that the process of deterioration becomes even more rapidly progressive. Finally, the main body of the anode is deprived totally of support, when the neck ruptures and the body separates from its hook and falls into the electrolyte. This may cause serious difficulties, such as a short circuit, or the dissolving of the anode in the electrolyte, causing a vast chemical imbalance. Obviating the problem of necking is therefore a very necessary and pressing one. Likewise the intergranular corrosion resulting from the attack by the electrolyte upon portions of the anode, resulting in the discharge of large crystal structures from the anode, may cause these crystals to fall into the electrolyte and be dissolved with equal chemical imbalance in the electrolyte. There is also the possibility of a pile-up of crystals and a shorting.

In order to counteract the deleterious effects of the rapid dissolution of portions of the anode creating sludge, constant filtrationof the electrolyte is usually resorted to in order to maintain a high degree of perfection of the electrodeposit. Such remedies are not entirely successful so the problem still remains of the continuing rapid pollution of the electrolyte. The pollution of the electrolyte also requires not only filtration, but analysis of the content of the bath to determine its composition and need for replenishment, thereby raising the cost of maintaining electrodeposition to accomplish plating of the desired degree of perfection. Efforts to reduce these problems by lowering the current density serve merely to prolong the plating process but, do not,

substantially improve the quality of the plate. There is still corrosion and sludging. The neck of the anode still deteriorates dimensionally.

Extruding of a consumable solder anode has been found to definitely produce a more suitable grain structure which is compatable to a degree with a longer life somewhat less necking, and less intergranular corrosion. But still, the problems persist in a lesser degree.

SUMMARY OF THE INVENTION It has been found that a consumable solder anode may be prepared which, when subjected to high current density for fast plating, when subjected to high and low pH electrolytes, nevertheless is highly resistant to necking, is highly resistant to intergranular corrosion, and is relatively free of surface accumulations of insoluble reaction products. An anode is prepared by any of the well-known methods such as extruding, rolling, drawing, extending, casting, forming, chill-casting or clading. The anode is composed of relatively pure tin and up to approximately percent lead. Not less than 20 p.p.m. calcium is added as a grain reducing material. As an alternative to calcium, phosphorus, tellurium and sulfur or combinations thereof may be substituted.

This anode is highly resistant to necking and has a much lesser degree, regardless of whether the electrolyte is of high or low pH and of very aggressive chemical character. The anode may be used at a high current density for faster solder plating because surface accumulations of insoluble reaction products are eliminated to a high degree. Thus, the constant checking of the composition of the electrolyte is no longer necessary, its frequent replenishment is not necessary, filtration need not be resorted to to remove the impurities that may appear in the electrolyte and impair its proper functioning. The plating accomplished is of a high degree of uniformity, and the ratio of tin and lead which characterizes the composition of the anode is reproduced on the work piece. The presence of the grain reducers accomplishes a vast reduction of the size of the crystal structure of the anode, so that the aggressive electrolytes do not succeed in rapidly undermining large crystals and introducing impurities into the electrolyte. Likewise, the refinement of crystal structure inhibits the necking of the electrode.

PREFERRED EMBODIMENTS Numerous compositions in accordance with the present inventions are possible.

EXAMPLE I Tin 5-lOO% Lead 0-95% Calcium, phosphorus, Sulfur,

Tellurium Not less than 20 p.p.m.

of any one or combination thereof EXAMPLE ll Tin Calcium Not less than 20 p.p.m.

EXAMPLE lll Tin 60% Lead 40% Calcium Not less than 20 p.p.m.

EXAMPLE IV Tin 5%" Lead 95% Sulfur Not less than 20 p.p.m.

In each of these examples, while 20 has been set forth as a minimum, it is preferable to use 50 to 100 p.p.m.

What is claimed is:

l. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or low pH electrolytes, surface accumulation of insoluble reaction products, or high current density, comprising:

a. preparing a solder anode consisting essentially of to 100 ppm calcium, and the remainder tin, and

b. electrodepositing solder from the anode on a work piece.

2. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or low pH electrolytes, surface accumulation of insoluble reaction products, or high current density, comprising:

a. preparing a solder anode consisting essentially of 20 to 100 ppm calcium and the remainder about 60 percent tin and about 40 percent lead, and

b. electrodepositing solder from the anode on a work piece.

3. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or low pH electrolytes, surface accumulation of insoluble reaction products, or high current density, comprising:

a. preparing a solder anode consisting essentially of 20 to 100 ppm sulfur and the remainder about 5 percent tin and about percent lead, and

b. electrodepositing solder from the anode on a work piece.

4. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or pH electrolytes, surface accumulation of insoluble reaction products, or high current density, comprising:

a. preparing a solder anode consisting essentially of 20 ppm of material selected from the group consisting of calcium, phosphorous, sulfur, or tellurium, and the remainder about 5 100 percent tin and about 0 95 percent lead, and

b. electrodepositing'solder from the anode on a work piece. 

2. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or low pH electrolytes, surface accumulation of insoluble rEaction products, or high current density, comprising: a. preparing a solder anode consisting essentially of 20 to 100 ppm calcium and the remainder about 60 percent tin and about 40 percent lead, and b. electrodepositing solder from the anode on a work piece.
 3. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or low pH electrolytes, surface accumulation of insoluble reaction products, or high current density, comprising: a. preparing a solder anode consisting essentially of 20 to 100 ppm sulfur and the remainder about 5 percent tin and about 95 percent lead, and b. electrodepositing solder from the anode on a work piece.
 4. The method of solder plating with a consumable solder anode subjected to necking, intergranular corrosion by high or pH electrolytes, surface accumulation of insoluble reaction products, or high current density, comprising: a. preparing a solder anode consisting essentially of 20 - 100 ppm of material selected from the group consisting of calcium, phosphorous, sulfur, or tellurium, and the remainder about 5 -100 percent tin and about 0 - 95 percent lead, and b. electrodepositing solder from the anode on a work piece. 